omerc.rst: fix example (fixes OSGeo#3794)

Author: rouault

docs/source/operations/projections/omerc.rst

@@ -100,7 +100,7 @@ Example: An approximation of the Danish "System 34" from :cite:`Rittri2012`
 
 ::
 
-    $ echo 10.536498003 56.229892362 | proj +proj=omerc +axis=wnu +lonc=9.46 +lat_0=56.13333333 +x_0=-266906.229 +y_0=189617.957 +k=0.9999537 +alpha=-0.76324 +gamma=0 +ellps=GRS80
+    $ echo 10.536498003 56.229892362 | cs2cs +proj=longlat +ellps=GRS80 +to +proj=omerc +axis=wnu +lonc=9.46 +lat_0=56.13333333 +x_0=-266906.229 +y_0=189617.957 +k=0.9999537 +alpha=-0.76324 +gamma=0 +ellps=GRS80
     200000.13   199999.89
 
 The input coordinate represents the System 34 datum point "Agri Bavnehoj", with coordinates